Another 273 question

This requires muuuuuuuch caution. Small engine, heavy waggon, plus it needs to carry a load.
You really have little room to move here with 273 cubes.
My suggestion would be the Edel 500 AVS2 carb [ annular primaries for great throttle response ] & the Isky E-4 cam suggested earlier.
Actually it's not that heavy now. I pulled the interior and just kept the front seat. I'm not looking for much power wise. Just a little more. The dual exhaust actually really helped with highway cruising. I am not going overboard. I like the idea of a smaller 500 cfm 4 barrel. I think the biggest issue would be exhaust manifolds/headers.